1. Field of the Invention
The present invention relates generally to exterior wall systems for commercial and residential structures. In another aspect, the invention concerns lightweight precast concrete wall panels.
2. Description of the Prior Art
Precast concrete wall panels have been used for years to provide durable and aesthetically pleasing exterior walls. One disadvantage of traditional precast concrete wall panels is the weight of the panels. The high weight of conventional precast wall panels can make them expensive to ship and erect. Further, because heavy wall panels cause deflection of structural steel wall members supporting the panels, the strength of the steel frame of a building may need to be increased in order to adequately support concrete wall panels without excessive deflection. Such a need to increase the strength of the structural steel members of a building can add significantly to the overall cost of the building.
In recent years, several lightweight alternatives to traditional precast concrete wall panels have been used. One such system is commonly known as EIFS (Exterior Insulation and Finish System). EIFS is a multi-layered exterior wall system that typically consists of a lightweight pliable insulation board covered with a fiberglass reinforced base coat that is coated with a colored acrylic finish coat. Although EIFS is lightweight and provides thermal insulation, a number of drawbacks are associated with EIFS. For example, EIFS walls have a tendency to crack and allow moisture to seep between the EIFS layers or between the innermost EIFS layer and the interior wall. In either case, such leakage can cause water damage and/or damage due to mold or mildew. In fact, the tendency of EIFS wall systems to leak has caused many insurance companies to stop writing policies covering EIFS structures. A further disadvantage of EIFS is its lack of durability. For example, simply bumping an EIFS wall with a lawn mower or other equipment during routine lawn maintenance can physically and visibly damage the EIFS wall, thereby necessitating expensive repair. Another problem with EIFS is the inability to form a true caulk joint at the edge of the wall. This inability to form a true caulk joint is caused by the fact that EIFS walls lack a sufficiently thick rigid edge. A proper caulk joint typically requires at least one inch of rigid edge so that a backer-rod can be inserted into a joint and a bead of caulk can fill the joint and seal against at least one half inch of the rigid edge. This allows the seal to maintain integrity during normal shifting and expansion/contraction of the structure. Thus, the lack of a true caulk joint in EIFS walls can contribute to moisture leakage.
Another lightweight wall system that has been introduced in recent years employs precast GFRC (Glass Fiber Reinforced Concrete) wall panels. GFRC wall panels are relatively strong compared to EIFS, but have a number of drawbacks. The main drawback of GFRC wall panels is expense. The making of GFRC wall panels is a labor intensive process wherein concrete and glass fibers are sprayed in a form. In addition to high labor costs associated with GFRC fabrication, the material cost of the glass fibers adds significantly to the overall cost of a GFRC wall panel.
Another relatively lightweight wall panel system that is being used today is commonly known as xe2x80x9cslender wall.xe2x80x9d Slender wall prefabricated wall panels typically include a relatively thin steel-reinforced concrete slab with structural steel framing rigidly attached to one side of the slab. A disadvantage of the slender wall system is that it requires the concrete supplier to fabricate the metal frame backup system, which requires a significant amount of design and fabrication time. Another disadvantage is that the inside face of the metal frame must be in near perfect alignment for proper drywall attachment.
Responsive to these and other problems, it is an object of the present invention to provide a lightweight, durable, and inexpensive prefabricated wall panel system.
A further object of the invention is to provide a light weight prefabricated wall panel of sufficient rigidity and thickness so that a proper caulk joint can be formed around the edge of the panel.
Another object of the invention is to provide a prefabricated wall panel system that can easily be attached to a thin metal framing member (e.g., a metal stud or C/Z purlin) of a support wall.
Still another object of the invention is to provide a lightweight concrete wall panel that is strong enough to withstand conventional handling and transporting methods without cracking.
Yet another object of the invention is to provide an improved method of constructing a wall using lightweight precast concrete wall panels.
It should be understood that not all of the above-listed objects need be accomplished by the present invention, and further objects and advantages of the invention will be apparent from the following detailed description of the preferred embodiment, the drawings, and the claims.
Accordingly, in one embodiment of the present invention, there is provided a lightweight precast wall panel comprising a concrete slab, a pair of elongated spaced-apart first channels, and a plurality of elongated spaced-apart second channels. The first channels extend substantially parallel to one another. The second channels extend substantially parallel to one another. The first and second channels are partially embedded in the slab and extend substantially perpendicular to one another. At least some of the second channels are disposed between the first channels.
In another embodiment of the present invention, there is provided a method of constructing a wall comprising the steps of: (a) erecting a support wall having a plurality of generally parallel spaced-apart elongated metallic outer wall framing members; (b) positioning a precast concrete wall panel adjacent the support wall, with the wall panel including a concrete slab, a pair of generally parallel spaced-apart elongated metallic side channels, and a plurality of generally parallel spaced-apart elongated metallic attachment channels, wherein the side channels and attachment channels extend substantially perpendicular to one another, at least some of the attachment channels are disposed between the side channels, and the side channels and attachment channels are partially embedded in the slab; and (c) coupling the wall panel to the support wall by extending self-tapping screws through the wall framing members and the attachment channels at attachment locations where the attachment channels and the framing members cross.
In still another embodiment of the present invention, there is provided a precast concrete wall system comprising a support wall, a precast wall panel, and a plurality of fasteners. The support wall includes a plurality of generally parallel spaced-apart elongated metallic framing members. The precast wall panel includes a concrete slab, a pair of generally parallel spaced-apart elongated metallic side channels, and a plurality of generally parallel spaced-apart elongated metallic attachment channels. The attachment channels are elongated in a direction that is substantially perpendicular to the direction of elongation of the side channels and the framing members. The side channels and attachment channels are partially embedded in the slab. The fasteners extend through the framing members and attachment channels at attachment locations where the framing members and attachment channels cross.